Physics 10: Additional HW 8 Problems


In addition to the problems from the book: 30.E.42, 27.E.10, 27.E.11, 27.E.15, 27.E.20, 27.E.29, 28.E.31, 28.E.33, the following four problems are a part of the required homework.

  1. If a particular uranium-235 nucleus undergoes fission, and in this instance produces barium-137 (137Ba) and zirconium-96 (96Zr) "daughter" nuclei, how many neutrons were spilled off in the split-up. Assume no nucleons are created or destroyed, and no protons pop out, but allow for the possibility that some neutrons transformed into protons within each of the daughter nuclei. It's not as hard as it sounds: really just a matter of counting nucleons.
  2. One mole (just think of it as a fixed, large number) of uranium-235 nuclei has a collective mass of 235.044 grams. Consider the hypothetical case wherein every one of these turns into xenon-134 (134Xe: mass = 133.906 grams) and molybdenum-98 (98Mo: mass 97.905 grams) plus three neutrons (mass 1.009 grams each). [In reality, there is variation in the product types].
    1. verify that the total number of nucleons (protons plus neutrons) is preserved in the transaction
    2. Figure out how much mass went missing?
    3. What percentage of the total starting mass ended up missing?
    4. Use E = mc2 to express this number in Joules.
  3. Starting with 116 moles of deuterium (mass per mole is 2.0141 grams, for a total mass of 233.636 grams) and fusing these to make 58 moles of helium-4 (mass per mole is 4.0026 grams for a total of 232.151 grams):
    1. How much mass is missing?
    2. What percentage of the total starting mass ended up missing?
    3. Using E = mc2, express this number in Joules
    4. Compare this to the energy from a similar starting mass of uranium to find how many times more energy one gets from fusion compared to fission (for similar mass inputs). Note: this is related to the steepness of the binding energy curve (lecture 22, slide 14) on the fusion side versus the gentle slope on the fission side.
  4. If typical chemical reactions (e.g., gasoline combustion) deliver about 40,000 Joules per gram:
    1. How many Joules would you get from 235 grams of gasoline?
    2. How much more potent is nuclear fission (problem 2) than gasoline? Express the answer as a ratio: fission delivers x times more energy. Be approximate (one significant digit).

Back to Physics 10 Main Page